Dear Anne, I'm very sorry to read your situation, the same thing happened to me last month. I'll try to answer your question with the information and experience I got:
As soon as your HGC levels drops, some of the familiar pregnancy symptoms like sore brests, vomiting etc CAN disappear but that's no "written law". Some women feel pregnant even when the baby stopped growing. My second u/s showed that the baby died about a week and a half before and I still felt everything. Also when there is just an empty sac your body can get confused and act like you are experiencing a normal healthy pregnancy.
At the moment I'm in a sort of in between situation: my m/c is almost 4 weeks ago and when I use my regular cycle I should expect AF on 12/6. I'm dealing with enlarged sore brests while just after the m/c I didn't had those, so it can be either a late effect of the m/c I had, an upcoming AF or a new pregnancy, since my doctor told me there was no problem in ttc right away.
Take care!
With my MC I had an U/S at 10 weeks...everything was measuring 7 and I was sure of my dates. My body never took care of this for those 3 weeks and I had to have a DNC. Sorry you are going through this good luck
I'm sorry, I don't know what to suggest other than getting a blood test. I actually had a MC where there was just an empty sac, but my levels were doubling.
Sorry you have to go through this.